The present application is based upon and claims priority to Japanese Application No. Hei 11-044792, filed Feb. 23, 1999, the entire contents of which is hereby incorporated by reference.
1. Field of the Invention
This invention relates to a fuel injection system for an engine, and more particularly to a fuel injection system suitable for an outboard motor engine.
2. Description of Related Art
In the interest of improving engine performance and particularly fuel efficiency and exhaust emission control, many types of engines now employ a fuel injection system for supplying fuel to the engine. Generally, in this system, fuel is injected into an air induction device or directly into a combustion chamber by a fuel injector. This fuel injection has the advantages of permitting the amount of fuel delivered for each cycle of the engine to be adjusted. In addition, by utilizing the fuel injection system, it is possible to maintain the desired fuel air ratio under a wide variety of engine running condition.
An amount of the fuel injected by the fuel injector is usually controlled by an ECU (Engine Control Unit) in response to the engine running conditions. More specifically, the fuel is delivered to the fuel injector by a fuel pump under a certain fixed pressure and duration for injection per unit time, i.e., a duty ratio, is controlled by the ECU so that any required amount of fuel can be metered.
The fuel injector generally has a construction shown in FIG. 1. This figure illustrates a cross-sectional view showing an exemplary fuel injector.
The fuel injector, designated generally by the reference numeral 30, includes an injector body 32. An opening 34 is pierced longitudinally through the body 32. A magnet core 36 is fixedly positioned at one side of the opening 34, while a plunger 38 is slidably supported within the opening 34 at the other side of the opening 34. The plunger 38 is biased by a coil spring 40 toward an end of the opening 34 and has a valve 42 that is seated on a valve seat 44 when urged by the spring 40. The plunger 38 and the valve 42 are unified to define a needle valve. The valve 42, therefore, closes the opening 34 when seated on the valve seat 44. The end of the opening 34 at the side where the valve 42 is disposed is narrowed to define an injection nozzle 46. A solenoid or electromagnetic actuator 48 is formed in the injector body 32 and surrounds respective portions of the magnet core 36 and plunger 38. Fuel is supplied into the opening 34 through an inlet portion 50 by a fuel pump and hence fills the opening 34 under a certain fixed pressure. A fuel filter 51 is provided at the inlet portion 50.
When the solenoid 48 is activated by the ECU, the magnetic core 36 and plunger 38 are magnetized. The plunger 38 then slides toward the magnetic core 36 against the biasing force of the coil spring 40. The valve 42 is parted from the valve seat 44 accordingly. Because the fuel fills the opening 34 under the certain pressure, it is sprayed from the nozzle 46 when the valve 42 is unseated. The ECU then ceases the activation of the solenoid 48 after a calculated duration. Hence, the valve 42 returns to the initial position where it is seated on the valve seat 44 and closes the opening 34, i.e., the injection nozzle 46, again.
As is apparent from the descriptions provided above, the fuel injector 30 is a normally closed type. Although this type is easy to be controlled relative to a normally open type injector, it gives rise to a problem if the engine is not operated for a certain period of time, particularly, under a high temperature condition.
The problem is that the fuel residual in the opening 34 will congeal if the fuel injector 30 does not spray the fuel for a relatively long period of time. That is, if the fuel is gasoline, it will evaporate and escape through a clearance between the valve 42 and the valve seat 44. However, impurities or heavy oil components that are intermixed in the gasoline will remain in the opening 34 and deposit on the valve 42 and valve seat 44. The deposit of the heavy oil components acts as a kind of adhesive and the valve 42 occasionally adheres to the valve seat 44. High temperature may expedite this situation. The longer the time in which the injector 30 remains idle, the stronger the degree of adhesion will be. Also, the higher the fuel pressure is, the harder the bond will be.
If the adhesion occurs, the fuel injector may not work and the engine consequentially cannot function properly. Occasionally, by pushing the valve 42 from the nozzle 46, the problem of this adhesion may be resolved. However, this manner of repair may damage the valve 42 and invite a need to dissemble and repair the fuel injector 30.
After the engine has started, the solenoid 48 is powered by a generator. However, at the moment of the engine starting, the generator is not driven by the engine and only a battery can supply power to the solenoid 48. The battery under this condition, however, must supply power also to other electrical equipment such as, for example, a starter motor and fuel pumps. As a consequence, the power to the solenoid 48 is reduced and the separation or release of the valve 42 from the valve seat 44 is more difficult when starting the engine.
Another type of fuel injector exists that has no magnet core. In this type, the plunger 38 is simply drawn by the solenoid when it is magnetized. However, the aforementioned problem also can occur in this type of fuel injector.
This problem is exacerbated when used on an outboard motor, as compared to other land vehicles. The engine for a land vehicle (e.g., an automobile) can easily be designed such that the injection nozzle 46 of the fuel injector 30 are directed downward. In this arrangement, the fuel residual may leak out through the valve clearance with its own weight. However, if the engine is applied to an outboard motor, it is somewhat difficult for the fuel residual to pass through the clearance because the fuel injector 30 is laid generally horizontally and the clearance is usually only about 50 to 100 xcexcm. Hence, the weight of the fuel residual does not help it pass through the clearance. Also, a drive unit of the outboard motor is arranged to be tilted up and down. When the drive unit is tilted up, in certain arrangement of the fuel injector 30, the injection nozzle 46 is directed upwardly. This arrangement aggravates the situation described above.
An aspect of the present invention thus involves the recognition that a need therefore exists for an improved fuel injection system that can easily release a valve from a valve seat in a fuel injector to ensure that the engine starts properly after a long period of non-use (i.e., inactivity).
In accordance with one aspect of the present invention, a fuel injection system is provided for an internal combustion engine. The engine has a cylinder body defining a cylinder bore in which a piston reciprocates. A cylinder head is affixed to an end of the cylinder body and defines a combustion chamber with the cylinder head and the piston. The fuel injection system comprises at least one fuel injector spraying fuel through at least one opening for supplying the fuel to the combustion chamber. The fuel injector includes a valve that is movable between a closed position and an open position to regulate fuel flow through the opening. An actuator mechanism includes at least one actuator that is coupled to valve to move the valve from the closed position. A first power supply is provided to supply power to the actuator under an normal operating condition of the engine. A second power supply is provided to supply greater power to the actuator than the power supplied by the first power supply. A switchover device is provided to selectively change the supply of power to the actuator between the first power supply and the second power supply.
In accordance with another aspect of the present invention, a fuel injection system is provided for an internal combustion engine. The engine has a cylinder body defining a cylinder bore in which a piston reciprocates. A cylinder head is affixed to an end of the cylinder body and defines a combustion chamber with the cylinder head and the piston. The fuel injection system comprises at least one fuel injector for spraying fuel to the combustion chamber. The fuel injector includes a valve and a valve seat on which the valve site. The fuel is sprayed only when the valve is unseated. A biasing mechanism biases the valve toward the valve seat so that the valve is normally seated on the valve seat. An actuator is provided to unseat the valve with an actuating force that acts against the biasing force of the biasing mechanism. The actuator is also adapted to unseat the valve with a separating force that is greater than the actuating force to separate the valve from the valve seat when the valve adheres to the valve seat.
In accordance with a further aspect of the present invention, an internal combustion engine comprises a cylinder body defining a cylinder bore in which a piston reciprocates. A cylinder head is affixed to an end of the cylinder body and defines a combustion chamber with the cylinder head and the piston. At least one fuel injector that sprays fuel through its opening is provided for supplying the fuel to the combustion chamber. The fuel injector includes a valve and a valve seat on which the valve site. The fuel is sprayed only when the valve is unseated. A biasing mechanism biases the valve toward the valve seat so that the valve is seated on the valve seat. Actuating means is provided for actuating the valve to be unseated with an actuating force that acts against the biasing force of the biasing means, and separating means is provided for separating the valve from the valve seat when the valve adheres to the valve seat with a separating force that is greater than the actuating force.
In accordance with a still further aspect of the present invention, a method is provided for controlling a fuel injection system. The fuel injection system has a fuel injector spraying fuel through at least one opening for supplying the fuel to a combustion chamber of an internal combustion engine. The fuel injector includes a valve closing the opening in its closing position under control of the control device. The method comprises actuating the valve with an ordinary force under normal operating conditions and actuating the valve with a separating force that is greater than the ordinary force when the valve remains in the closing position when the ordinary force is applied.
Further aspects, features and advantages of this invention will become apparent from the detailed description of the preferred embodiments and variations thereof that follow.